KR20070079633A - Apparatus and method for selecting cell in a mobile communication system consisting different network - Google Patents

Abstract

An apparatus and a method for selecting a cell in a mobile communication system having heterogeneous networks are provided to determine registration to a 3G system or a 2G system by using a preset flag value in case of selecting a cell after downward handover. A control part of a dual mode terminal, if interRAT(Radio Access Technology) handover from a 3G system to a 2G system is completed, sets an "ISHO_flag_for_LU" flag, a system downward handover flag, to "1" and executes communication in the 2G system(300,302). Then, if a call end signal is inputted from a keypad, the control part completes the call with the 2G system(304). Afterwards, the control part receives and decodes a BCCH(Broadcast Control CHannel)(306), and checks whether an SI2quater parameter has been decoded from the BCCH(308). If so, the control part, based on the decoded SI2quater parameter, judges whether cell reselection is required(312). In case cell reselection is required, the control part resets the system downward handover flag to "0"(318), and then executes location update procedures and routing area update procedures in the 3G system(320,322).

Description

Apparatus and method for cell selection in mobile communication systems with heterogeneous networks {APPARATUS AND METHOD FOR SELECTING CELL IN A MOBILE COMMUNICATION SYSTEM CONSISTING DIFFERENT NETWORK}

1 is a control flowchart of selecting a cell after handover in a dual mode terminal capable of providing a WCDMA scheme and a GSM scheme;

2 is an internal block diagram of a dual mode terminal to which the present invention is applied;

3 is a control flowchart of cell selection after handover from a 3G system to a 2G system according to an exemplary embodiment of the present invention.

The present invention relates to an apparatus and method for selecting a cell in a mobile communication system, and more particularly, to an apparatus and method for selecting a cell in a mobile communication system having a heterogeneous network.

In general, a mobile communication system is a system developed to provide a voice communication service to a user without restriction of location and distance. In such a mobile communication system, various multiple access methods have been proposed in order to allow multiple users to communicate at the same time. Looking at these multiple access methods as an example, there are various methods such as a time division multiple access scheme, a frequency division multiple access scheme, and a code division multiple access scheme.

As described above, according to various multiple access methods, mobile communication systems have evolved into different types of systems. Initially, mobile communication systems using time division multiple access and frequency division multiple access among the multiple access schemes were developed in Europe. In the United States and Korea, which are represented by the North American scheme, code division multiple access schemes are used. Mobile communication systems have been developed. Various types of mobile communication systems have been gradually developed from the initial form of providing only a voice service to a form of providing a data service as well as voice. This development of mobile communication system is due to the rapid development of technology and the desire of users to receive more data faster.

As the technology changes, communication protocols for each system are newly changed. This is because the types of services to be provided and their configurations are different. Therefore, each terminal providing a service to a user must provide various communication protocols according to changes of systems. In addition, service providers providing mobile communication services must simultaneously provide the old service until all terminals can receive a new service or until a legally stipulated time. Therefore, the terminal providers produce and provide a dual mode terminal having a communication protocol of a system for providing a previous service and a system for providing a new service.

Here, the dual mode terminal refers to a terminal capable of operating in all systems having different communication protocols. These dual mode terminals should be provided with handover between different networks (hereinafter referred to as "heterogeneous network"), and should be able to communicate with each network.

Meanwhile, in a mobile communication system, a terminal should select a cell where it is located when initial power is turned on or when moving from a specific region to another region. Here, the cell means an area of the base station. Therefore, the term "cell" as used herein refers to the entire area of a base station in the case of an omni base station and a specific sector of the base station in the case of a sector type base station.

However, as described above, in the mobile communication system having heterogeneous networks, dual-mode terminals are generally configured to select a cell that provides a better service when selecting a cell. In the following description, for convenience of description, a system that provides an improved service is referred to as a "first system", and a system that does not otherwise referred to as a "second system".

The terminal searches for a cell of the first system first and selects a cell capable of providing the service of the first system when initial power is applied or when moving to another area due to a movement without performing communication. do. If the cell of the first system does not exist, the cell of the second system is searched for and selected. In addition, in a mobile communication system having a heterogeneous network, a handover may be performed when a communication service that can be provided by both the first system and the second system, such as a voice service, is provided.

Let's take a look at the actual example. For example, dual mode is provided in a Global System for Mobile communication (GSM) system, a European second generation (2G) system, and a Wideband Code Division Multiple Access (WCDMA) system, a third generation (3G) system. A case in which a call is terminated after a handover of a call is made in a terminal will be described.

If a handover is made between the GSM system and the WCDMA system, it is not necessary to return to any system after performing a handover to a specific system. Therefore, the dual mode terminal performing the handover from the GSM system to the WCDMA system can maintain the cell of the WCDMA system as the serving cell. In addition, the dual-mode terminal performing the handover from the WCDMA system to the GSM system can maintain the cell of the GSM system as a serving cell. Here, the serving cell refers to a cell that receives a service and performs a procedure for continuously registering a location and receiving the service thereafter.

However, in practice, companies that manufacture dual-mode terminals use a method of leaving a cell of a 3G system as a serving cell if a 3G system exists rather than a 2G system. Then, the procedure performed in the dual mode terminal when the handover as described above will be described with reference to FIG.

FIG. 1 is a control flowchart of selecting a cell after handover in a dual mode terminal capable of providing a WCDMA scheme and a GSM scheme.

In the case of FIG. 1, a procedure is performed in a state where a handover is completed from a cell of a 3G system to a cell of a 2G system while performing a voice call in a dual mode terminal supporting both 2G (GSM) and 3G (WCDMA). to be. Accordingly, the procedure is a procedure performed in a state in which a call is completed in a GSM call connection state after an InterRAT (Radio Access Technology) handover from a cell of a 3G system to a 2G system.

When the call is completed, in step 100, the terminal performs a location update procedure on the GSM network. Thereafter, the terminal proceeds to step 102 and sequentially performs a routing area update procedure. After that, the UE measures the strength of the signal received from the WCDMA neighbor cell according to the SI2quater, which is already received system information in step 104, and proceeds to step 106, where the WCDMA neighbor cell is an InterRAT cell reselection criterion. Check if it is satisfied. Such inspection may be performed by satisfying the conditions as shown in Table 1 below.

    <WCDMA to GSM InterRAT cell reselection criterion> If RLA_C <Qsearch_I, the measurement of 3G cell is performed. Qsearch_I is received in SI2quater * Criterion 1.RSCP> FDD_Qoffset + RLA_C of Serving cell (GSM) 2.RSCP> FDD_Qoffset + RLA_Cn where n = 0,1. k where k is the number of suitable neighboring cells 3.Ec/No> = FDD_Qmin The above condition should be satisfied for the period of 5 seconds FDD_Qoffset = FDD_Qoffset + 5dB When the cell reselection is occurring within previous 15 seconds

If the cell reselection condition is satisfied, the UE proceeds to step 108 and performs interRAT cell reselection from the cell of the 2G system to the cell of the 3G system. On the other hand, if the cell reselection condition is not satisfied as a result of step 106, the process proceeds to step 110 to perform the GSM mode.

However, after performing InterRAT handover from the 3G system to the 2G system in the weak electric field of the 3G system cell instantaneously, when the GSM call is disconnected, the neighbor cell of the strong 3G system is idle in the idle state. Although present, no InterRAT cell reselection is performed from the cell of the 3G system to the cell of the 2G system. That is, as described above with reference to FIG. 1, an InterRAT cell reselection is performed after the location update procedure and the routing area update procedure are sequentially performed in the 2G region. At this time, if the update fails during the location update process or the routing area update process in the cell area of the 2G system, the terminal retries for location update or routing area update. If this retry occurs, the InterRAT cell reselection time from the cell of the 2G system to the cell of the 3G system takes 20-30 seconds longer.

In addition, a waste of air resources occurs due to signaling by location update or routing area update in the 2G domain. In extreme cases, there may be no response from the network when registering a location on a 2G system. In this case, the terminal may not receive a voice call or data call received for 20-30 seconds.

Accordingly, an object of the present invention is to provide an apparatus and method for fast cell selection in a mobile communication system having a heterogeneous network.

Another object of the present invention is to provide a cell selection apparatus and method capable of preventing waste of radio resources in a mobile communication system having a heterogeneous network.

Another object of the present invention is to provide an apparatus and method for selecting a cell that can increase a service reception rate in a mobile communication system having a heterogeneous network.

Apparatus of the present invention for achieving the above object is a device for cell selection in a mobile terminal capable of communicating with a heterogeneous network, a wireless unit capable of transmitting and receiving data over the heterogeneous network and the radio; ; A memory having a handover flag area; Control to demodulate and decode the signal received from the radio, control to encode and modulate a signal to be transmitted to a base station, control the setting of a system down handover flag during system down handover during the communication, and And a control unit for controlling to receive and decode a broadcast control channel for a predetermined time when the termination ends, inspecting parameters for cell reselection, and controlling the radio unit to control uplink system registration when uplink system registration is possible.

The method of the present invention for achieving the above objects is a cell selection method after the system down handover in a dual-mode terminal of a mobile communication system having a heterogeneous network, the system down handover flag when the system down handover occurs during communication And setting up a communication method, performing a communication, checking a parameter for cell reselection by decoding a broadcast control channel for a predetermined time when the communication is terminated, and checking whether uplink system registration is possible; As a result, if the upstream system registration is possible, a process of performing upstream system registration is included.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

2 is an internal block diagram of a dual mode terminal to which the present invention is applied. Hereinafter, an internal block configuration and operation of the dual mode terminal according to the present invention will be described in detail with reference to FIG. 2.

The control unit 211 controls the overall operation performed in the mobile phone, and in particular, controls the wireless unit 212 to receive a signal according to a corresponding system to provide a dual mode. In addition, the control unit 211 controls the cell selection according to the present invention. Control of such cell selection is further examined in the control flow chart described below.

The wireless unit 212 converts a radio frequency (RF) signal received from the antenna ANT into a baseband signal under the control of the control unit 211, and transmits a signal received to the control unit 211 through the wireless unit 212. It converts into a radio frequency (RF) signal and transmits it to the air. The wireless unit 212 is composed of a wireless module for providing a dual mode. The controller 211 controls demodulation, deinterleaving, and decoding operations according to characteristics of the signals received from the wireless unit 212, and outputs the audio signal to the speaker SKP through the audio input / output unit 213 in the case of a voice signal. In addition, the control unit 211 converts the electrical voice signal received from the microphone MIC of the audio input / output unit 213 into a digital signal, encodes, interleaves, and modulates it, and outputs it to the wireless unit 212. When various control data necessary for communication are input to the control unit 211, the control unit 211 performs encoding and modulation thereof and provides the same to the wireless unit 212. In addition, the control unit receives the control signals provided from the wireless unit 212 and demodulates and decodes them and provides them to the control unit 211.

The memory 215 stores a program required for a mobile phone and a control program according to the present invention. Also stores various data set by the user and the ISHO_flag_for_LU flag bit stored according to the present invention. The ISHO_flag_for_LU flag bit bit sets the flag when a handover occurs from a 3G system to a 2G system during communication. Detailed description thereof will be further described in the control flowchart described later. In addition, the memory 215 may include an area for driving a timer according to the present invention. If the memory 215 does not have a timer area, a separate timer should be provided or provided in the controller 211 described above.

The display unit 216 may be configured as a liquid crystal display panel, and provides various graphic user interfaces (GUIs) required by the user under the control of the controller 211. In addition, the display unit 216 may include a vibration motor, a lamp, and the like to notify the incoming call of the mobile phone. In addition, the display unit 216 may display a network that is currently connected and is receiving a service. The keypad 117 has a key metric structure and generates a key value input by the user and provides the generated key value to the controller 111.

3 is a control flowchart of cell selection after handover from a 3G system to a 2G system according to an exemplary embodiment of the present invention. Hereinafter, a control process when selecting a cell according to the present invention will be described in detail with reference to FIGS. 2 and 3.

The controller 211 illustrates that an InterRAT handover occurs to the 2G system while performing communication in the 3G system in step 300. Since the above process is generally a matter of the handover procedure provided in the mobile communication system having a heterogeneous network, it will not be described in detail here. When the handover of step 300 is completed, the controller 211 proceeds to step 302 and sets the "ISHO_flag_for_LU" flag, which is a newly added flag, to 1 according to the present invention. This flag is hereinafter referred to as a "system down handover flag". In addition, the controller 211 performs a communication in the GSM system, which is a 2G system, after setting the system down handover flag to 1 in step 302. After performing the communication as described above, the controller 211 performs a call termination signal by the user's request, that is, when the call termination signal is received from the keypad 217 or when the call termination signal is received from the GSM system, which is a 2G system. Proceed to end the call with the GSM system.

After that, the controller 211 proceeds to step 306 to control the radio 212 to receive and decode a broadcast control channel (BCCH). Thereafter, the controller 211 proceeds to step 308 and checks whether the SI2quater parameter is decoded from the broadcast control channel. If the SI2quater parameter is not decoded, the process proceeds to step 310 and determines whether the preset timer has expired. In the control flowchart of the present invention, the setting of the timer is not shown. The timer may be set when the SI2quater parameter is first decoded or checked when decoding the broadcast control channel. Therefore, the timer value can be implemented differently in each case. In the embodiment of the present invention, it will be assumed that the timer is set to 5 seconds. In addition, the timer may be implemented through the memory 215 of FIG. 2, may be implemented to be processed in the controller 211, or may be configured to include a separate timer. The controller 211 proceeds to step 318 if the timer expires as a result of check 310 and proceeds to step 306 to continue decoding the broadcast control channel.

On the other hand, if the SI2quater parameter is decoded in step 308, the controller 211 proceeds to step 312 and determines whether to reselect the cell using the decoded SI2quater parameter. When reselecting the test result cell in step 312, the controller 211 proceeds to step 318. Otherwise, the controller 211 proceeds to step 314 and performs location update in the GSM system, which is a 2G system. After that, the controller 211 proceeds to step 316 to perform a Routing Area Update (RAU) procedure on the 2G system.

On the other hand, when proceeding from step 312 to step 318, the control unit 211 resets the system down handover flag according to the present invention back to zero. This is because when the handover occurs from the 3G system to the 2G system next time, the same operation as the control flow of the present invention can be performed. After resetting the system down handover flag as described above, the controller 211 proceeds to step 320 to perform a location update procedure on the 3G system, and proceeds to step 322 to perform a routing area update procedure on 3G.

As described above, an operation of performing a location registration and routing area update procedure to the 3G system after communication is terminated in the 2G system area is referred to as an "upward system registration process".

As described above, the system down handover flag according to the present invention is newly added, and the flag is set whenever a handover occurs from the 3G system to the 2G system during communication. Accordingly, when the call is disconnected from 2G, the UE may quickly perform interRAT cell reselection from the 2G system to the 3G system.

As described above, after the InterRAT handover from the 3G system to the 2G system, the system down handover flag is set to (ISHO_Flag_for_LU) = 1, and when the call is terminated in the 2G system, the 5 second timer is operated as in the embodiment of the present invention. . Then, the terminal operation continues until the SI2quater is decoded, and when the SI2quater information is obtained, InterRAT cell reselection is performed from the 2G system to the 3G system. As a result of this, if the interRAT cell reselection criterion is satisfied, the location registration and routing area update is performed in the 3G system to prevent the unnecessary registration of the location in the 2G system. In other words, the uplink system registration process is performed by determining a possible case.

In addition, when the call of the 2G system is disconnected after the InterRAT handover from the 3G system to the 2G system, the serving cell, the neighbor cell, and the 3G neighbor cell are measured, and the system information is decoded. After that, it takes about 4 to 5 seconds to transmit a Location update request message. In this embodiment, the timer is set to 5 seconds. Therefore, finding a SI2quater using a timer does not cause the problem of delaying normal operation.

As described above, in the mobile communication system having a heterogeneous network, when a cell is selected after system downlink handover is performed, it is quickly determined by registering a 3G system or a 2G system using a preset flag value. The cell can be selected, and there is an advantage of preventing waste of radio resources. In addition, since the cell selection is faster, there is an advantage of increasing the reception efficiency of the call.

Claims (5)

A method of cell selection after system down handover in a dual mode terminal of a mobile communication system having a heterogeneous network, When a system down handover occurs during communication, setting a system down handover flag and performing communication; Checking a parameter for cell reselection by decoding a broadcast control channel for a predetermined time when the communication ends and checking whether uplink system registration is possible; If the uplink system registration is possible as a result of the check, the cell selection method in a mobile communication system having a heterogeneous network comprising the step of performing the uplink system registration. The method of claim 1, wherein the heterogeneous network, A cell selection method in a mobile communication system having a heterogeneous network, characterized in that it comprises a base station of a second generation network, a GSM system, and a third generation network of a WCDMA system. The method of claim 2, The method of selecting a cell in a mobile communication system having a heterogeneous network, further comprising: performing a location registration and a routing area update procedure at a base station of a GSM system when uplink system registration is impossible. The method of claim 2, wherein the uplink system registration, A cell selection method in a mobile communication system having a heterogeneous network, comprising: performing a location registration and routing area update procedure with a base station of a WCDMA system. An apparatus for cell selection in a mobile terminal capable of communicating with a heterogeneous network, A wireless unit for transmitting / receiving data over the heterogeneous network and wirelessly, demodulating and decoding the received signal, and controlling encoding and modulation of a signal to be transmitted to a base station; A memory having a handover flag area; Controls the setting of the system down handover flag during system down handover during communication through the wireless unit, and controls to receive and decode a broadcast control channel for a predetermined time when the communication is terminated, thereby inspecting a parameter for cell reselection. And a control unit controlling the radio unit to control uplink system registration when uplink system registration is possible.

Images